Preparation And Characterization Of Polystyrene Nano-films

Nano-films of polystyrene (PS) with different molecular weight were produced by the methods of spin coating and droplet deposited evaporation at room temperature from extremely dilute solution. Characterization and analysis of these samples were accomplished with the using of atomic force microscopy (AFM). This paper focused on the influences that various processing parameters (such as solution concentration and molecular) gave to the properties of ultrathin films. The mechanism of preparation methods was also intensively researched. And the shapes of PS molecules from very dilute concentration exist in particles were studied finally.The results show that at lower concentration, particles have smaller dimensions and the number of particles per area decreases sharply when the concentration comes to very dilute. Calculated maximum number of molecular chains in average particle from extremely dilute solution is least but it is still far from the single chain state. The approximation in the simulation, the tip convolution of AFM and aggregation of PS molecules during film forming lead to the results.Particle films produced by spin coating possess good uniformity, yet the other method prepares more non-uniform morphology and the uniformity becomes worse when it turns to higher molecular weight. This is the mechanism of two different preparation methods that causes the phenomenon above. The dimensions are directly proportional to molecular weight and the rising trend with Mw is more significant in droplet deposited evaporation. However, negative correlation between degree of aggregation per particle and molecular weight is presented.The surface roughness of nano-films progressively increases with solution concentration, and there are not apparent differences between roughness and selection of molecular weight or method used. Therefore, concentration is a key factor of roughness among these parameters.PS molecules spin coated are more inclined to ellipsoid and this is more obvious at higher Mw while simulation result of molecules deposited approaches sphere. These are also the differences between principles of the two methods that account for the results. These are all delineated in the paper.